Although I don't think anything will really match up to what WoW has done for gamers, it's still a very virgin field. I think there's a lot of room for people to make money in the MMO field.

The only game type that's going to beat WoW is a modern day setting, without the witchcraft/magic aspect to it. It's going to have to be the opposite of what WoW's setting is, and the mechanics of game play, character development, items and abilities are gonna have to be really refined (so they're gonna be three times better then what they are now).

Other then that, I see WoW leaving the scene when the "Greatest" next game comes, but that's not gonna be for a while.

Hypothetical of course, but it's what I see comin.